Servo boosters

ABSTRACT

The present invention relates to a tandem fluid-pressure servo booster comprising a housing, a rigid internal wall within the housing, and a movable wall on each side of the rigid wall, defining four chambers axially spaced within the housing, there being a plurality of fluid passageways between an internal surface of the housing and the periphery of the rigid wall connect a first pair of said chambers, and a plurality of tubular ducts within the housing connect a second pair of said chambers, said tubular ducts each having one end located in the rigid internal wall and passing through the peripheral regions of one of the movable walls.

United btates Patent 1 1 1 1 E Re 1 Weatherhogg Reissued Aug. 5, 1975 i1 SERVO BOOSTERS [56] References Cited [75] Inventor: Charles BrianWeatherhogg, UNITED STATES PATENTS Harbome, land 3,289,547 12/1966 Kytta92/48 x [73] Assignee: Girling Limited. Birmingham,

England Primary Examiner--Martm P. Schwadron Assistant Examiner-AbrahamHershkovitz [:3] Flled: Sept 1974 Attorney, Agent, or Firm-ScrivenerParker Scrivener 1211 Appl. No.: 510,705 and Clarke Related U.S. PatentDocuments ABSTRACT Reissue of: The present 'n em 11 relates t a tandemfl d 1 v 10 0 ul [64] f 2 23 97 4 pressure servo booster comprising ahousing, a rigid I g internal wall within the housing, and a movablewall if i J 15 1972 on each side of the rigid wall, defining fourchambers e axially spaced within the housing, there being a plurality offluid passageways between an internal surface of [30] ForelgnApphcauonlprmmy Data the housing and the periphery of the rigid wallcon- June I7, 1971 Un ted K ngdom 28365/71 nect a fi pair of saidchambers and a m of Oct. 2i. 1971 United Kingdom 48882/71 bu|ar ductswithin the housing connect a second pair of said chambers, said tubularducts each having one [51] U.S. Cl. 92/48; 92/94; 92/97 end heated inthe rigid intern n and passing [51] Int. Cl. F01!) 19/00 through theperipheral regions of one of the movable [58] Field of Search 92/48, 49,63, 64, 94,

23 Claims, 9 Drawing Figures 6 Sheets-Sheet 1 no Nmu Q MN PM OWN Reissue5, 1915 6 Sheets-Sheet a Reissued Aug. 5, 1975 6 Sheets-Sheet 5 ReissuedAug. 5, 1915 6 Sheets-Sheet 4.

--- mes-- Reissued Aug. 5, 1915 6 Shams-Sheet 6 v: g Q

1 SERVO aoosraas Matter enclosed in heavy brackets I 1 appears in theoriginal patent but forms no part of this reissue specification; matterprinted ln ltalics indicates the additions made by reissue.

The present invention relates to tandem fluidpressure servo boosters andhas particular application to a tandem fluid-pressure servo booster foruse with a vehicle braking system.

Tandem fluid-pressure servo boosters are known and generally comprise ahollow casing having a rigid internal wall with a movable wall on eachside thereof, said rigid and movable walls defining four separatechambers axially spaced within the casing. The first and third chambers,along the axis of the housing, are connected for common pressureconditions, the second and fourth chambers are connected for commonpressure conditions, and both movable walls are connected to a commonoutput member.

in tandem fluid pressure boosters of the type described above all fourchambers are maintained at substantially uniform pressure when thebooster is inoperative and the second and fourth chambers are chargedwith pressure fluid, e.g., air, to cause mutual displacement of the twomovable walls when the device is operated.

According to the present invention a tandem fluidpressure servo boostercomprises a housing, a rigid internal wall within the housing, a movablewall on each side of the rigid wall, said walls defining four chambersaxially spaced within the housing, a plurality of fluid passagewaysbetween an internal surface of the housing and the periphery of therigid wall connecting a first pair of said chambers, and a plurality oftubular ducts, within the casing, connecting a second pair of saidchambers, said tubular ducts each having one end located in the rigidinternal wall and passing through the peripheral regions of one of themovable walls.

Preferably each movable wall comprises a flexible diaphragm andaccording to this aspect of the present invention, the tubular ductspass through an enlarged peripheral region of a flexible diaphragm.Preferably the enlarged peripheral region of the diaphragm through whichthe tubular ducts pass includes an inwardly directed lip in sealingengagement with the internal rigid wall.

According to a further aspect of the present invention a tandemfluid-pressure booster comprises a housing having a rigid internal wallseparating two movable walls to define four chambers axially spacedwithin the housing, said rigid wall having a radial flange at itsperipheral region which flange engages and seals a peripheral region ofone of the movable walls against an annular ring seated within thehousing.

Preferably fluid pressure passages connecting two of the chambers forcommon pressure conditions are defined between the annular ring andinternal surfaces of the housing.

According to another aspect of the invention, said first pair ofchambers are interconnected by way of one or more passageways extendingaxially of the booster housing between an internal surface of thehousing and the periphery of said rigid wall, and one or more radiallyextending holes located in said rigid wall and communicating with saidpassageways.

Preferably, the periphery of at least one of the flexible diaphragms isheld against a shoulder on the rigid wall by means of an annular band.

Preferably, the annular band embraces anaxially extending portion ofsaid diaphragm periphery from which extend a plurality of tongues whichengage in respective recesses in the rigid wall.

Advantageously, the peripheral portion of the diaphragm has an outersurface which is provided with one or more teeth, or tooth-likeprojections, which are adapted to engage the inner surface of saidannular band to inhibit removalof the band therefrom.

in a preferred embodiment, the rearward flexible diaphragm is located bythe annular band, said shoulder being formed on an axially extending,peripheral flange portion of said rigid wall.

The two movable walls are conveniently connected to a common output rodand according to this aspect of the present invention a tandemfluid-pressure servo booster comprises a housing having an internalrigid wall and two movable walls separated by the rigid wall to definefour chambers axially spaced within the housing, pressure fluidpassageways connecting a first pair of said chambers and pressure fluidducts connecting a second pair of said chambers, an axially extendingrod connecting both movable walls and constituting a com mon output rod,a first one of said movable walls being axially located on the commonoutput rod by a sleeve member and said movable wall presenting anaxially extending resilient lip sealingly engaged with the sleeve.

Preferably the sleeve passes through the rigid internal wall and aflexible seal is provided between the internal wall and the sleeve.Conveniently the seal between the rigid internal wall and the sleevecomprises an annular sealing member, restrained in a recess in the rigidwall by spring means, and an axially extending lip engaged with theexternal diameter of the sleeve.

According to a further aspect of the present invention a tandemfluid-pressure servo booster comprises a housing having an internalrigid wall separating two movable walls to define four chambers axiallyspaced within the housing, one of the said flexible walls being insealing engagement with an axially extending output shaft by means of atwin-lipped seal, the outer diameter of the seal engaged with theinternal diameter of the movable wall being greater than the greatestinternal diameter of the seal between the two seal faces engaging therod.

The present invention also envisages a method for assembling a tandemfluid-pressure servo booster comprising a housing having a rigidinternal wall and a movable wall on either side thereof, said wallsdefining four chambers axially spaced within the housing, and accordingto this aspect of the present invention a method of assembling thebooster comprises the steps of assembling the three walls on an axialassembly with a return spring for the movable walls positioned betweenone flexible wall and the rigid wall, inserting the assembly into asplit housing, and then connecting together the housing parts.

Preferably the axial assembly includes a common output for the twomovable walls and the valve body for the booster.

By positioning the movable wall return spring between one flexible walland the rigid wall of the assembly, the method proposed by the presentinvention allows all the internal parts for the booster to be assembled,tested and inspected before being assembled in the housing.

The invention will now be described further by way of example withreference to the accompanying drawings, in which:

FIG. 1 shows a section through a tandem fluidpressure servo booster onthe line II-II of FIG. 2;

FIG. 2 shows a partial end view of the booster of FIG. 1 in thedirection of the arrow A;

FIG. 3 shows a partial end view of the booster of FIG. 1 in thedirection of the arrow B,

FIG. 4 shows a vertical section through the rigid wall of the boostershown in FIGS. 1, 2 and 3;

FIG. 5 shows an end view of the rigid wall in the direction of the arrowC of FIG. 4;

FIG. 6 shows the other end view of the rigid wall in the direction ofthe arrow D of FIG. 4;

FIG. 7 is a center line section through a second embodiment of a tandemservo-booster constructed in accordance with the present invention;

FIG. 8 is a sectional detail, circled and referenced A in FIG. 7, of theembodiment of FIG. 7 to an enlarged scale, illustrating the manner inwhich the rear diaphragm is located relative to the fixed partitionmemher; and

FIG. 9 is a further sectional detail of the embodiment of FIG. 7 to anenlarged scale, illustrating the manner in which the front diaphragm islocated relative to the fixed partition member.

The tandem fluid pressure servo booster illustrated in FIGS. 1, 2 and 3comprises a housing 11 constructed from two sheet metal shells 12 and 13united, in a manner to be described hereinafter, at a peripheral regionThe shell 12 comprises an end wall 15, cylindrical wall 16, and a flange17 upstanding from wall 16. The end wall has a central opening definedby a lip 18 and a cup-shaped member 19 is inserted into the opening andsupported in fluid tight engagement with end wall 15 by a seal 20between lip 18 and the member 19.

The shell 13 comprises a cylindrical wall 21 and an end wall, generallyindicated by numeral 22, which wall 22 has a central opening defined byan axially extending boss 23 within which a valve body 24 is located.The cylindrical wall 21 includes six angularly spaced regions 25 whichtaper inwardly of the housing towards the end wall 22 and said sixregions 25 are thus angularly separated by six radially disposed ribs26. The regions 25 blend into arcuate shoulders 27, lying in a commonplane perpendicular to the axis of the housing, and said shoulders 27form a seat for a ring 28 which comprises a cylindrical wall 29 adaptedto tit snugly against the internal surfaces of the region 25 when aradial flange 30 of ring 28 abuts the shoulders 27. The six radial ribs26 thus form fluid passages passing outwardly of the ring 28 betweensaid ring 28 and the internal surface of ribs 26.

A first movable wall comprises a diaphragm 31 which has an enlargedperiphery 32 seated in the ring 28 and its inner region secured insealed engagement with a flange portion 33 of the valve body 24. Thediaphragm 31 also has a thickened annular region 34 engageable with anoutwardly extending flange 35 of a cup-shaped member 36 located betweendiaphragm 31 and the end wall 22 of shell 13. Cup-shaped member 36 isperferated to allow unrestricted flow of air therethrough.

A rigid wall or partition 37 has an axially extending flange 38 whichabuts the enlarged periphery 32 of diaphragm 31 and a second movablewall, comprising a diaphragm 39 with an enlarged periphery 40, has itsenlarged periphery 40 in abutment with the periphery of partition 37 onthe side opposite to the flange 38. The flange 17 of shell 12 is enteredinto the open side of shell 13 and secured therein by a crimpingoperation along region 14 so that the periphery 40 of diaphragm 39, theflange 38 of rigid partition 37 and the enlarged region 32 of diaphragm31 are sandwiched together and retained between the flange 17 and ring28.

It should be observed from the drawing that the enlarged peripheralregion 32 of diaphragm 31 has an axially directed lip 32a which engagesin a peripheral recess 38a in the flange 38. Further, the enlargedperiph eral region 40 of diaphragm 39 is located in a tapered recessbetween the flange 38 and flange 17, the tapered recess wideningoutwardly from the axis of the device, and the peripheral region 40 isshaped to fit snugly into the tapered recess.

The position of the ring 28 is fixed by its abutment with the shoulders27 and as the flange 38 is rigid the axial loading pressure applied tothe shells 12 and 13 is absorbed entirely by the peripheries 32 and 40.The peripheral region of the diaphragms 31 and 39 are thus axiallyloaded and this loading in combination with the shape of the peripheries32 and 40, resist displacement of the diaphragms from their peripherallocations.

The flange 38 in providing a seat for the peripheral region 32 ofdiaphragm 31 serves a further purpose in that it prevents the diaphragmregion 32 from expanding into or otherwise obstructing the passagewaysformed by the ribs 26..

A common output rod 41 is disposed in the housing 11 and passes axiallyin succession through the member 19, an annular plate 42 supporting thediaphragm 39, the diaphragm 39, rigid partition 37, a fulcrum plate 43,a finger plate 44 contacting the inner surface of diaphragm 31,diaphragm 31, and into the valve body 24. A sealing member 45, retainedin cup-shaped member 19 by a ring 46, forms a fluid pressure sealbetween member 19 and the push rod 41.

The rod 41 has a sleeve 47 supported thereon and the sleeve 47 abutsfulcrum plate 43 at one end face and plate 42 at the other end face. Aspring ring 48 in an annular groove 41a in rod 41 retains plate 42against the adjacent end face of sleeve 47.

The diaphragm 39 presents an axially extending lip 49 in sealingengagement with the sleeve 47 and an annular sealing member 50, housedin a recess 51 in the rigid partition 37, presents an annular axiallyextending lip 52 in sealing engagement with the sleeve 47. Sealingmember is retained in recess 51 by a spring ring 53.

The innermost regions of the fingerplate 44 are restrained axially onone side by a spring register 54 and an annular sealing member 55defines a seal between spring register 54 and the rod 41. The sealingmember 55 is a double lip seal and the maximum internal diameter 56between the lips is less than the minimum diamemost regions of theflanges of fingerplates 44 and the end face of the valve body 24.

The rod 41 is slidably disposed in a bore 59 of valve body 24 and ascrew 60, having an enlarged head greater in diameter than the diameterof bore 59, is screwed axially to the end of the rod 41. The head ofscrew 60 is located in an enlarged bore region of valve body 24 and thesocket head 61 of a ball joint connection is engaged against an internalshoulder 62 of valve body 24 so as to be normally spaced from screw 60.The socket head 61 is retained in valve body 24 by a tubular sleeve 63and an actuating rod 64 presents a ball end 65 which is housed in thesocket 61 to complete the ball and socket connection.

A flexible seal 66 extends between the outer end of sleeve 63 and theboss 23 of end wall 22.

The diaphragm 39 defines a movable wall for a first chamber 67 to theleft side of the diaphragm 39, as seen in FIG. 1, and the movable wallof a second chamber 68 between the diaphragm 39 and the rigid partition37. The diaphragm 31 defines, in combination with rigid partition 37, athird chamber 69 and a fourth chamber 70 is defined bythe diaphragm 31,and end wall 22.

The chambers 67 and 69 are connected for common pressure conditions bytubular ducts '7 1 arranged in three groups, each of two ducts 71,housed in three angularly spaced ribs 72 on cylindrical wall 16 of shell12. The tubular ducts 71 extend through shaped slots 73 in the enlargedperiphery 40 of diaphragm 39 and into passageways 74 in the axiallyextending flange 38 of partition 37. The passageways 74 opening into thechamber 69 so that chambers 67 and 69 are open in communication throughpassageways 74 and the ducts 71.

The chambers 68 and 70 are connected by the pressure fluid passagesbetween annular ring 28 and the six radial ribs 26, and slots 75, cut inthree angularly spaced regions of the outer periphery of the flange 38of partition 37, and thus fluid pressure passages are provided betweenchambers 68 and 70 to maintain said chambers in open communication.

A connection 76 at end wall allows chamber 67, and thereby chamber 69,to be continuously connected to a low pressure source (not shown).

The tandem fluid-pressure servo booster described above with referenceto the drawings operates as follows:

In the normal inoperative position for the booster illustrated in FIG. 1the actuating rod 64 adopts the position shown in FIG. 1 with the sockethead 61 spaced from the screw 60. The flange 58 of sealing member 55 isresting on an annular valve seat 77 on flange 33 of valve body 24 toprevent flow of air from the interior of valve body 24 into the housing11. At the same time flange 58 is unseated from an annular valve seat 78on flange 33 so that the interior of chamber 70 communicates withchamber 69 by way of passageways 79 through flange 33, between valveseats 77 and 78, openings between the fingers of finger plate 44 andholes 80 in the fulcrum plate 43.

The connection 76 maintains chamber 67 in communication with the lowpressure source and thus chamber 67, and chamber 69 communicatingtherewith, are maintained at a substantially constant low pressure. Thechamber 70, and chamber 68 in open communication therewith, is open tochamber 69 through passageways 79 so that all the chambers 67, 68, 69and are established and maintained at a substantially uniform lowpressure.

A spiral compression spring 81 between partition 37 and fulcrum plate 43urges the fulcrum plate 43 and thereby diaphragms 31 and 39 into theinoperative position illustrated and a coil compression spring 82 actsbetween fulcrum plate 43 and spring register 54 tensions flange 58against the valve seat 77.

When the booster is to be actuated, actuating rod 64 is advanced towardsthe left (as seen in FIG. 1) so that socket head 61 and sleeve 24 arealso moved towards the left. The movement of sleeve 24 towards the leftis resisted by spring 81 acting on fulcrum plate 43 and spring 82 actingon spring register 54 the actual force exerted by spring 82 is less thanthat of spring 81 so that initial movement of sleeve 24 causes thefingers of finger plate 44 to bend about the annulus of contact with thefulcrum plate 43, the deflection of the fingers increases as the sleeve24 moves towards the left until eventually the flange 58 of sealingmember 55, engages the second annular valve seat 78. In this position ofthe assembly the flange 58 of sealing member 55 is seated on bothannular valve seats 77 and 78.

Further movement of the valve body 24 causes both annular valve seats 77and 78 to act on flange 58 causing further bending of the deflectingfingers of finger plate 44 and as the inclination of the fingersincreases the pressure between valve seat 77 and flange 58 reduces untileventually flange 58 lifts off the valve seat 77.

When flange 58 lifts off valve seat 77 atmosphere flows through thehollow sleeve 63, passageways 83 in the socket head 61, and by way ofpassageways 84, parallel to rod 41, to the internal end face of theflange 33 of valve body 24. The air at the end face of flange 33 flowsbetween the valve seat 77 and the unseated flange 58 and throughpassageways 79 into the cup-shaped member 36 so as to act against theright-hand side of diaphragm 31. The diaphragm 31 disengages fromengagement with flange 35 of cup shaped member 36 and an air flow intochamber 70 is thus established.

The air flow into chamber 70 increases the pressure in chamber 70 andair flow by way of the passageways around annular ring 28 and throughthe slots 75, in the periphery of partition 37 into chamber 68 wherebyboth chambers 70 and 68 experience an increase in internal pressure.

As air flows into chambers 68 and 70 diaphragms 39 and 31 are urgedtowards the left as seen in FIG. 1, diaphragm 31, through finger plate44, acting against fulcrum plate 43 and diaphragm 39 acts through plate42 and sleeve 47 on fulcrum plate 43 to urge both moving walls 31 and39, the sleeve 47, fulcrum plate 43, and the rod 41 towards the left asseen in FIG. 1 against the resistance of spring 81.

The actual displacement of rod 41 is utilized to cause a desireddisplacement, such as operation of the master cylinder of a vehiclebraking system! and when rod 41 is connected to the piston of the mastercylinder the master cylinder piston will be subject to the samedisplacement as the rod 41.

Displacement of rod 41 towards the left continues with continueddisplacement of the actuating rod 64 towards the left. When thedisplacement of rod 64 is terminated the force exerted on the diaphragm31 outwardly of the contact annulus of fulcrum plate 43 acts on thefingers ring 44 to cause the fingers to deflect so that flange 58 againseats on both annular valve seats 77 and 78 whereby the system is heldin a substantially locked position.

When the actuating rod 64 is moved towards the right as seen in FIG. 1valve body 24 also moves towards the right, the air pressure in chamber70 acting on the finger ring 44 in combination with the relief ofpressure on flange 58 due to the displacement thereof, caused thefingers to deflect such that flange 58 is unseated from valve seat 78and seats on valve seat 77 to terminate the flow of air from theinterior of the valve sleeve 24 into chamber 70. At the same time theunseating of flange 58 from seat 78 whereby the air in chambers 70 and68 flow from said chambers through the passageways 79 in flange 33,between the fingers of the finger plate 44, through openings 80 in thefulcrum plate 43 and thus into chamber 69.

Thus during the return of valve body 24 all the chambers communicatewith the low pressure source and are brought to a substantially uniformlow pressure.

As the air pressure in chamber 70 and 68 falls the return spring 81urges fulcrum plate 43 away from partition 37, fulcrum plate 43 actsdirectly on finger plate 44 to displace diaphragm 31 towards the rightand. by way of the connection of annular plate 42 with sleeve 47 tofulcrum plate 43 the diaphragm 38 is moved back towards the startposition. The movement of the valve body towards the right causes rod 41to be retracted and displacement of the moving part towards the rightcontinues until all the parts are returned to the start positionillustrated in FIG. 1.

It would be seen from the illustrated embodiment that the control rod 41can be assembled with the valve body 24 (by the screw 60) and thebooster elements can be axially assembled on the rod 41 before theassembly is inserted into the casing 11.

With construction according to the invention, the return spring 81 islocated between the fulcrum plate 43 and the rigid wall or partition 37so that the whole of the internal assembly can be built up, inspectedand tested before the assembly is inserted into the casing 11. Themethod of sandwiching the peripheral regions 32 and 40 of the twodiaphragms on either side of the annular flange 38 between the ring 28and flange 17 allows the periphery of both diaphragms 31 and 39 to beequally stressed and restrained.

The construction of the tandem servo-booster embodiment shown in FIGS.7, 8 and 9 of the drawings is basically the same as that of theembodiment illustrated in FIGS. 1 to 6 and like reference numerals havetherefore been used to denote identical parts in the two embodiments.The embodiment shown in FIGS. 7, 8 and 9 differs from the firstembodiment primarily in two portions of the booster, namely the means bywhich a permanent connection is achieved between the chambers 68 and 70,and the means by which the peripheral bead of the rear diaphragm 31 islocated relative to the housing 1 1.

In the second construction, the slots 75 are replaced by one or moreholes 110 which extend radially through a solid portion 112 of the rigidhousing portion 37. As illustrated in F IG. 9, the forward facingsurface 113 of the partition member 37 forms an effective seal with therearward facing surface 115 of the diaphragm peripheral portion 40. Asin the case of the slots 75, the holes 110 communicate with fluidpassages 114 defined between the radially outer surface 116 of theaxially extending flange 38 of the rigid housing partition 37 and theinner surfaces of the six ribs 26 in the cylindrical housing wall 21.

Clearly the number and groupings of the radially extending holes arecapable of considerable variations. For example, (i) a single such hole110 can be provided which communicates with a single passageway 114corresponding to the provision of a single rib 26; (ii) a plurality ofholes 110 can communicate with a plurality of passageways 1 14; (iii) aplurality of holes 110 can communicate with a single passageway 114; anycombination of (i), (ii) and (iii) can be provided at circumferentiallyspaced locations around the periphery of the booster housing.

In the first embodiment, the outer enlarged portion 32 (bead) of thediaphragm 31 is constrained between the rearward end of the axiallyextending partition flange 38 and the annular ring 28 which abuts theshoulders 27 formed by the housing wall. Although the bead 32 has anaxially directed lip 32a which engages in a peripheral recess 38a in theflange 38 and which provides a certain amount of radial retention forthe bead, the arrangement is such that the retention predominantly actsagainst displacement of the bead in an axial direction.

In the second embodiment, the peripheral portion 118 of the diaphragm 31is no longer in the form of a fat, annular head but is considerablythinner in its radial dimension, having a cross-section which isgenerally rectangular, as shown in the drawing, This peripheral portion1 18 extends axially of the booster housing and embraces a reduceddiameter end portion 120 of the flange 38. Over the majority of itslength, the outer end of the peripheral portion 118 engages a radiallyoutwardly extending shoulder 122 provided on the flange 38. However, atcircumferentially spaced intervals, the peripheral portion 118 isprovided with axially extending tongues 124 which are thicker in theradial direction than the remainder of the peripheral portion 118. Eachtongue 124, of which there are 10 in this case, is received in arespective recess 126 in the shoulder 122 of the flange 38.

The peripheral portion 118 of the diaphragm 31 is held in position onthe reduced diameter portion 120 of the flange 38 by an annularretaining band 128 of rectangular section. As shown in FIG. 8, the outersurface 130 of the peripheral portion 118 is provided with one or moretooth-like projections 132 which are firmly gripped by the peripheryportion 118 in a manner to inhibit removal of the diaphragm therefrom.One axial end of the band 128 is engaged by a shoulder 134 in thehousing 11 and the other axial end engages the tongues 124 to firmlylocate the tongues in position in their respective recesses 126.

The peripheral portion 118 is connected to the main portion of thediaphragm 31 by way of a radially extending portion 136 which is locatedbetween the housing shoulder 134 and the rear end surface 138 of theflange 38.

In the above described manner, the peripheral portion 1 18 is positivelylocated relative to the housing 1 1 in both an axial and a radial sense,the tongues 124 engaged in the recesses 126 preventing rotation of thediaphragm 31 relative to the housing 11.

The aforegoing second construction enables the overall diameter of thebooster housing to be reduced,

Re. 28.50l

which factor can be critical in some vehicle installations.

ln respect of all other features of construction and operation, thesecond embodiment is substantially identical to the first embodiment.

I claim:

1. A tandem fluid-pressure servo booster comprising a housing. a rigidinternal wall within the housing, a movable wall on each side of saidrigid internal wall, said walls defining four chambers axially spacedwithin the housing, a plurality of fluid passageways defined between aninternal surface of said housing and the periphery of said rigidinternal wall connecting a first pair of said chambers, and a pluralityof tubular ducts, within said housing, connecting a second pair of saidchambers, said tubular ducts each having an end region located in saidrigid internal wall and passing through peripheral regions of one of thesaid movable walls.

2. A tandem fluid-pressure servo booster as claimed in claim 1 andwherein said movable wall through which the tubular ducts pass,comprises a flexible dia phragm.

3. A tandem fluid-pressure servo booster as claimed in claim 2 andwherein said flexible diaphragm includes an enlarged peripheral region.

4. A tandem fluid-pressure servo booster as claimed in claim 3 andwherein said enlarged peripheral regions of said flexible diaphragms areaxially retained between an internal shoulder defined by the housing andsaid rigid internal wall.

5. A tandem fluid-pressure servo booster as claimed in claim 3 andwherein the tubular ducts pass through the enlarged peripheral regionsof the diaphragm.

6. A tandem fluid-pressure servo booster as claimed in claim 1 andwherein said rigid internal wall includes inclined surfaces which seatagainst inclined surfaces in the peripheral region of the movable wallthrough which said tubular ducts pass.

7. A tandem fluid-pressure servo booster comprising a housing, a rigidinternal wall within the housing, a movable wall on each side of therigid wall, said walls defining four chambers axially spaced within thehousing, a plurality of fluid passageways between an internal surface ofthe housing and the periphery of the rigid wall connecting a first pairof said chambers, and a plurality of tubular ducts, within the casing,connecting a second pair of said chambers, said tubular ducts eachhaving one end located in the rigid internal wall and passing throughthe peripheral regions of one of the movable walls and wherein the rigidinternal wall has a flange extending axially away from the tubularducts.

8. A tandem fluid-pressure servo booster as claimed in claim 7 andwherein the tubular ducts lie substantially parallel to the axis of thebooster and the rigid internal wall includes radial and axial passagesopening to the tubular ducts and to the chamber adjacent the rigid walland remote from said ducts.

9. A tandem fluid-pressure servo booster as claimed in claim 7 andwherein the movable wall through which the tubular ducts pass includesan inwardly directed lip in sealing engagement with the rigid internalwall.

10. A tandem fluid-pressure servo booster as claimed in claim 7 andwherein the tubular ducts are arranged in groups and said groups arespaced circumferentially about the peripheral regions of the rigidinternal wall.

11. A tandem fluid-pressure servo booster as claimed in claim 7 andwherein the tubular ducts each have one end located in the rigidinternal wall and said flange is in scaling engagement with theperipheral regions of the movable wall remote from the tubular ducts.

12. A tandem fluid pressure servo booster according to claim 7 whereinsaid flange engages and seals a peripheral region of one of the movablewalls against an annular ring seated within the housing.

13. A tandem fluid-pressure servo booster as claimed in claim 12 andwherein said flange has its outer end region reduced in diameter toenter into an axially extending peripheral flange on the movable wallremote from said tubular ducts.

14. A tandem fluid-pressure servo booster as claimed in claim 12 inwhich the movable wall remote from the tubular ducts has an enlargedperipheral region which is axially retained between the flange of theinternal wall and an annular ring seated within the housing, saidannular ring defining a cylindrical Wall and a radial flange, theperipheral regions ofthe movable wall being seated within thecylindrical wall and the radial flange being seated against radialshoulders within the hous- 15. A tandem fluid-pressure servo booster asclaimed in claim 12 and wherein an axially extending peripheral flangeon the movable wall is held in position on the reduced end of the flangeof the rigid internal wall by an annular retaining band.

16. A tandem fluid-pressure servo booster as claimed in claim 15 andwherein said axially extending peripheral flange on the movable wallincludes at least one annular projection upstanding from the outersurface of said flange and the annular retaining band engages saidannular projection to inhibit removal of the peripheral flange from theflange of the rigid internal wall.

17. A tandem fluid-pressure servo booster as claimed in claim 12 inwhich the peripheral flange of the movable wall includes axiallyextending tongues which are received in respective recesses in theflange of the rigid internal wall and said tongues have a thickness, inthe radial direction, greater than the thickness of the remaining partsof said peripheral flange.

18. A tandem fluid-pressure servo booster comprising a housing, a rigidinternal wall within the housing, a movable wall on each side of saidright internal .vall, said walls defining four chambers axially spacedlthin the housing, an axially extending flange on sait rigid wall thehousing includes ribs defining fluid p .ssageways radially outwardly ofa flange of the rigid internal wall and passing radially over a unionbetween said flange and a movable wall engaged thereon, said fluidpassageways connecting a first pair of said chambers, and a plurality oftubular ducts, within said housing. connecting a second pair of saidchambers, said tubular ducts each having an end region located in saidrigid internal wall and passing through the peripheral regions of one ofthe movable walls.

19. A tandem fluid-pressure servo booster as claimed in claim 18 andwherein the face of the rigid internal wall remote from the flangeincludes radial slots connecting the said fluid passageways with thatchamber between said slotted side of said rigid internal wall and themovable wall adjacent thereto.

20. A tandem fluid-pressure servo booster as claimed in claim 18 inwhich the fluid passageways are connected to the chamber between theside of the rigid internal wall remote from the flange and the movablewall adjacent thereto by holes passing substantially radially throughthe peripheral regions of the said rigid internal wall.

21. A tandem fluid-pressure servo booster as claimed in claim 18 inwhich the housing comprises two metal shells connected together atcooperating peripheral regions and peripheral regions of said twomovable walls and said internal rigid wall are clamped axially betweenradial shoulders of the two shells.

22. A tandem fluid-pressure servo booster comprising a housing, a rigidinternal wall within the housing and a movable wall on each side of saidrigid internal wall, said walls defining four chambers axially spacedwithin the housing, a plurality of fluid passageways defined between aninternal surface of said housing and the periphery of said rigid wallconnecting a first pair of said chambers and a plurality of axiallyextending fluid ducts connecting a second pair of said chambers, anaxially extending rod connecting both movable walls and constituting acommon output rod, said axially extending ducts being radially spacedfrom the axis of said output rod, a first one of said movable wallsbeing axially located on the common output rod by a sleeve member andsaid movable wall presenting an axially extending resilient lipsealingly engaged with the sleeve.

23. A tandem fluid-pressure servo booster as claimed in claim 22 andwherein the sleeve passes through the rigid internal wall and a flexibleseal is provided between the internal wall and the sleeve.

1. A tandem fluid-pressure servo booster coMprising a housing, a rigidinternal wall within the housing, a movable wall on each side of saidrigid internal wall, said walls defining four chambers axially spacedwithin the housing, a plurality of fluid passageways defined between aninternal surface of said housing and the periphery of said rigidinternal wall connecting a first pair of said chambers, and a pluralityof tubular ducts, within said housing, connecting a second pair of saidchambers, said tubular ducts each having an end region located in saidrigid internal wall and passing through peripheral regions of one of thesaid movable walls.
 2. A tandem fluid-pressure servo booster as claimedin claim 1 and wherein said movable wall through which the tubular ductspass, comprises a flexible diaphragm.
 3. A tandem fluid-pressure servobooster as claimed in claim 2 and wherein said flexible diaphragmincludes an enlarged peripheral region.
 4. A tandem fluid-pressure servobooster as claimed in claim 3 and wherein said enlarged peripheralregions of said flexible diaphragms are axially retained between aninternal shoulder defined by the housing and said rigid internal wall.5. A tandem fluid-pressure servo booster as claimed in claim 3 andwherein the tubular ducts pass through the enlarged peripheral regionsof the diaphragm.
 6. A tandem fluid-pressure servo booster as claimed inclaim 1 and wherein said rigid internal wall includes inclined surfaceswhich seat against inclined surfaces in the peripheral region of themovable wall through which said tubular ducts pass.
 7. A tandemfluid-pressure servo booster comprising a housing, a rigid internal wallwithin the housing, a movable wall on each side of the rigid wall, saidwalls defining four chambers axially spaced within the housing, aplurality of fluid passageways between an internal surface of thehousing and the periphery of the rigid wall connecting a first pair ofsaid chambers, and a plurality of tubular ducts, within the casing,connecting a second pair of said chambers, said tubular ducts eachhaving one end located in the rigid internal wall and passing throughthe peripheral regions of one of the movable walls and wherein the rigidinternal wall has a flange extending axially away from the tubularducts.
 8. A tandem fluid-pressure servo booster as claimed in claim 7and wherein the tubular ducts lie substantially parallel to the axis ofthe booster and the rigid internal wall includes radial and axialpassages opening to the tubular ducts and to the chamber adjacent therigid wall and remote from said ducts.
 9. A tandem fluid-pressure servobooster as claimed in claim 7 and wherein the movable wall through whichthe tubular ducts pass includes an inwardly directed lip in sealingengagement with the rigid internal wall.
 10. A tandem fluid-pressureservo booster as claimed in claim 7 and wherein the tubular ducts arearranged in groups and said groups are spaced circumferentially aboutthe peripheral regions of the rigid internal wall.
 11. A tandemfluid-pressure servo booster as claimed in claim 7 and wherein thetubular ducts each have one end located in the rigid internal wall andsaid flange is in sealing engagement with the peripheral regions of themovable wall remote from the tubular ducts.
 12. A tandem fluid pressureservo booster according to claim 7 wherein said flange engages and sealsa peripheral region of one of the movable walls against an annular ringseated within the housing.
 13. A tandem fluid-pressure servo booster asclaimed in claim 12 and wherein said flange has its outer end regionreduced in diameter to enter into an axially extending peripheral flangeon the movable wall remote from said tubular ducts.
 14. A tandemfluid-pressure servo booster as claimed in claim 12 in which the movablewall remote from the tubular ducts has an enlarged peripheral regionwhich is axially retained between the flange of the internal wall and anannular ring seated within the housing, said annular ring defining acylindrIcal wall and a radial flange, the peripheral regions of themovable wall being seated within the cylindrical wall and the radialflange being seated against radial shoulders within the housing.
 15. Atandem fluid-pressure servo booster as claimed in claim 12 and whereinan axially extending peripheral flange on the movable wall is held inposition on the reduced end of the flange of the rigid internal wall byan annular retaining band.
 16. A tandem fluid-pressure servo booster asclaimed in claim 15 and wherein said axially extending peripheral flangeon the movable wall includes at least one annular projection upstandingfrom the outer surface of said flange and the annular retaining bandengages said annular projection to inhibit removal of the peripheralflange from the flange of the rigid internal wall.
 17. A tandemfluid-pressure servo booster as claimed in claim 12 in which theperipheral flange of the movable wall includes axially extending tongueswhich are received in respective recesses in the flange of the rigidinternal wall and said tongues have a thickness, in the radialdirection, greater than the thickness of the remaining parts of saidperipheral flange.
 18. A tandem fluid-pressure servo booster comprisinga housing, a rigid internal wall within the housing, a movable wall oneach side of said right internal wall, said walls defining four chambersaxially spaced within the housing, an axially extending flange on saidrigid wall the housing includes ribs defining fluid passageways radiallyoutwardly of a flange of the rigid internal wall and passing radiallyover a union between said flange and a movable wall engaged thereon,said fluid passageways connecting a first pair of said chambers, and aplurality of tubular ducts, within said housing, connecting a secondpair of said chambers, said tubular ducts each having an end regionlocated in said rigid internal wall and passing through the peripheralregions of one of the movable walls.
 19. A tandem fluid-pressure servobooster as claimed in claim 18 and wherein the face of the rigidinternal wall remote from the flange includes radial slots connectingthe said fluid passageways with that chamber between said slotted sideof said rigid internal wall and the movable wall adjacent thereto.
 20. Atandem fluid-pressure servo booster as claimed in claim 18 in which thefluid passageways are connected to the chamber between the side of therigid internal wall remote from the flange and the movable wall adjacentthereto by holes passing substantially radially through the peripheralregions of the said rigid internal wall.
 21. A tandem fluid-pressureservo booster as claimed in claim 18 in which the housing comprises twometal shells connected together at cooperating peripheral regions andperipheral regions of said two movable walls and said internal rigidwall are clamped axially between radial shoulders of the two shells. 22.A tandem fluid-pressure servo booster comprising a housing, a rigidinternal wall within the housing and a movable wall on each side of saidrigid internal wall, said walls defining four chambers axially spacedwithin the housing, a plurality of fluid passageways defined between aninternal surface of said housing and the periphery of said rigid wallconnecting a first pair of said chambers and a plurality of axiallyextending fluid ducts connecting a second pair of said chambers, anaxially extending rod connecting both movable walls and constituting acommon output rod, said axially extending ducts being radially spacedfrom the axis of said output rod, a first one of said movable wallsbeing axially located on the common output rod by a sleeve member andsaid movable wall presenting an axially extending resilient lipsealingly engaged with the sleeve.
 23. A tandem fluid-pressure servobooster as claimed in claim 22 and wherein the sleeve passes through therigid internal wall and a flexible seal is provided between the internalwall and the sleeve.